Build

Docker Compose Tip #32: Build contexts and dockerignore patterns

Speed up builds and reduce image size by managing build contexts effectively. Don’t send unnecessary files to the Docker daemon! Understanding build context The build context is what gets sent to Docker daemon: services: app: build: . # Current directory is the context # Everything in . gets sent to daemon! Check your context size: # See what's being sent docker build --no-cache . 2>&1 | grep "Sending build context" # Output: Sending build context to Docker daemon 458.2MB 😱 Custom build contexts Specify different contexts for different services: ...

Docker Compose Tip #23: Multi-platform builds with platforms

Build once, run everywhere! Create images that work on ARM Macs, Intel servers, and Raspberry Pi with a single build command. Configure multi-arch builder Docker Desktop handles this by default. For other Docker installations, set up buildx: # Only needed if not using Docker Desktop # Create and use a new builder docker buildx create --name multiarch --use # Verify available platforms docker buildx ls Configure platforms Specify target architectures in your compose file: ...

Docker Compose Tip #12: Using target to specify build stages

One Dockerfile, multiple environments. Use target to build only the stage you need - faster builds, smaller images, cleaner separation. The basics Multi-stage Dockerfile: # Development stage FROM node:20-alpine AS development WORKDIR /app COPY package*.json ./ RUN npm install COPY . . CMD ["npm", "run", "dev"] # Production stage FROM node:20-alpine AS production WORKDIR /app COPY package*.json ./ RUN npm ci --only=production COPY . . RUN npm run build CMD ["npm", "start"] Target specific stages in compose.yml: ...

Docker Compose Tip #4: Using SSH keys during build

Need to access private Git repositories during build? Here’s how to do it securely with SSH. The setup Enable SSH forwarding in your compose.yml: services: app: build: context: . ssh: - default # Uses your default SSH agent Or use specific keys for different services: services: app: build: context: . ssh: - github=/home/user/.ssh/github_key # Custom key for GitHub - gitlab=/home/user/.ssh/gitlab_key # Different key for GitLab The Dockerfile Use BuildKit’s SSH mount to clone private repos: ...